1. Field of the Invention
This invention relates generally to a device used in the interventional treatment of neurological disorders, and more particularly to a novel electrode lead securing member which mounts to a burr hole in the patient""s skull and prevents undesirable translation of the implanted lead as the external portion of the lead is manipulated during surgery.
2. Description of the Prior Art
The use of electrical stimulation of the brain for the purposes of alleviating pain and the treatment of other neurological afflictions has been utilized for a number of years, and in many instances has become the standard of care. The technique comprises the implantation of a long flexible electrical lead through a burr hole in the patient""s skull, and into electrical contact with the pathological section of the patient""s brain. The flexible lead comprises a plurality of long hetically wound wires encased in a elastomeric sheath. The distal end of the wire leads include electrical contacts and are placed in the brain. The proximal end of the wire leads remain external to the skull, and is coupled to an extension connector which joins the electrical wires to an electrical generator.
As is clear from the delicacy of the surgical field, it is critical to utilize robust instruments and implants which are not easily broken, and which do not lend themselves easily to unwanted movements. In particular, when an electrode lead is implanted, the position of the active tip is critical. The effects of the field generated by the electrical contacts is highly position dependent, and as a result, movement of the electrode after proper positioning can reduce or eliminate all effectiveness of the treatment. As it can be a very tedious process to find the appropriate location within the brain for the active tip, it is also critical that once the lead is situated, it should not be moved accidentally. Many of the subsequent manipulations of the external portions of the electrode leads, however, must be carried out after the active tip has been properly positioned. It is, therefore, a considerable concern that there be a means of securing the implanted portion of the electrode relative to the skull and the brain, while permitting the external portion to be moved freely. The additional feature which should be considered is that the surgeon should be able to easily manipulate any such securing device with ease, even when covered in slippery bodily fluids.
A device which is presently available in the art is illustrated in FIG. 1. This device 10 is intended to hold a flexible wire lead 12 from moving, but is not designed to seat in a hole in the patient""s skull. Rather, it is designed to be secured to soft tissue (for example in the vacinity of the spinal column). The use of this device is, therefore, intended to prevent gross movement of the electrode lead 12. It is comprised of a first receiving member 14 which is cylindrical in shape. The lower portion of the cylinder forms a tapered hole 16 having an opening which is approximately the same diameter as the electrode lead 12. A second inner seating member 18 fits within the receiving member, also having an axial bore through which the electrode lead passes. The tip 20 of the seating member 18 is thin-walled, such that the channel formed therethrough may deflect inward if compressed. The second, seating member is permitted to translate within the receiving member 14 from an an open position which permits the lead 12 to freely slide through the assembly, to a closed disposition in which the tip is forced into the narrowed end 16 of the bore of the receiving member 14. In this position, the lead is friction locked in place by the compressed walls of at the tip of the seating member 18. The exterior surface of the receiving member further includes a series of through holes 20 which permit the assembly to be secured to adjacent tissue by sutures. Unfortunately, the device is very difficult to manipulate in a surgical environment as it requires manual pushing and pulling of small members which are seated within one another, and which have no defined open and closed dispositions which demonstrably indicate that the electrode lead is truly secure.
A more directly related device which is presently available in the art is illustrated in FIG. 2, and is described in U.S. Pat. No. 5,464,446. It comprises a first port member 22 which is cylindrical and seats in the burr hole formed in the patient""s skull 24. The exterior lateral surface of the port includes a contoured circumferential flange portion 26 which is intended to form a seal with the inner lateral surface 28 of the burr hole. The upper portion of the port member includes an outwardly extending rim 30 which seats against the exterior surface of the skull 30 around the edge of the burr hole when the port is inserted fully in the burr hole. This upper contour is also designed to mate with a cap section 32. The central axis of the seating member 22 forms a channel through which the electrode 34 seats and can slide prior to being locked in place. The cap 32 has a pair of channels formed therein; a first 36 which extends axially along the same direction as the axial passage in the port member, and the second 38 which extends out radially along the undersurface. The cap 32 engages the upper contour (and requires a suture 40 to hold the members together) in such a way that the electrode lead is compressed and is thereby locked in place. The use of a suture to secure the electrode, even indirectly, is a considerable drawback as it is difficult to manipulate, not easily reversible, and does not provide a readily obvious means for ensuring that the lead is truly secured against movements when the external portion is manipulated during the remainder of the surgery. Also, the compression lock, as in the first example is not easily viewed as it happens under the cap member.
The objects of the present invention are, therefore, clearly to provide an electrode securing assembly which reliably, easily, reversibly, and obviously locks an electrode lead to the skull, and most importantly, prevents the unwanted movement of the implanted portion of a deep brain stimulation lead during the manipulation of the external portion after the active internal tip has been properly positioned.
More specifically, it is an object of the present invention to provide an assembly which reliably mates with a burr hole in the skull and secures an electrical lead such that it does not move within the skull, but which permits free manipulation of the portion of the electrical lead which is external to the skull.
Simultaneously, it is also an object of the present invention to provide a mechanism which is easily manipulated by the surgeon under the conditions of the surgical field.
The preceeding objects of the invention are provided by the present device which comprises a first cylindrical port member which seats into a burr hole in the skull, and a second electrode lead locking member which is bayonet locked within the port member. More particularly, the port member includes an outer surface contour which grips the inner surface of the burr hole, and a laterally extending upper lip which seats against the outer rim of the burr hole in the patient""s skull. The inner surface of the port member further includes a bayonet lock receiving structure, which generally comprises a pair of diametrically opposed recesses. Corresponding laterally extending elements on te external surface of the lead locking portion are provided to fit in these recesses such that but inserting and rotating the lead locking member, it is secured within the port member. Further, the second electrode lead locking member includes a central axial channel through which the electrode is passed, and which may slide through the channel freely prior to being locked therein.
The upper portion of the lead locking member includes a sliding element which may be manipulated easily between an offset position and an occluding position. These alternate dispositions, and more particularly, the movements between them, are transverse to the axis of the member and the orientation of the electrode. Specifically, the sliding element is a disc which is seated in the upper surface of the lead locking member. The disc is initially offset relative to the hole which is the terminus of the axial channel. The disc slides along a track in the upper surface of the member into a closed position which partially blocks the hole. In this occluding position, the sliding member partially narrows the channel, and if there is an electrode lead extending therethrough, the lead is squeezed by the sliding member and thereby prevented from continued relative motion. The sliding member, or disc, may include at least one small recess into which a tool may be inserted to facilitate the translation between the open and closed positions. The track in which the sliding member translates, may further include a tab, ratchet, catch, or other structural feature by which the surgeon/user may readily recognize if the sliding element has ben fully engaged at the open or closed position.
Unlike prior devices, two of which are described above, the manipulation of the locking mechanism of the present invention is readily visible to the user, as it involves the translation of a sliding member transverse to the axial channel at the upper surface of the lead locking member. This feature may prevent additional mistakes associated with incomplete fixation of the lead in the locking mechanism.
The present device also resolves the difficulty of use which is a limitation of the prior art devices. By providing recesses in which a tool, for example a scissors, plyers, or other hand-held retractor, may engage and manipulate the mechanism, the present invention eliminates a substantial drawback to using similar prior art devices.
In addition, the reversibility of the locking mechanism is very easy to achieve, i.e. simply reversing the bias of the sliding element away from the hole or rotating and removing the lead locking member from the port member, is a substantial advance over semi-permanent securing means which require sutures to secure the assembly to the adjacent tissue, and sutures to hold a lead locking cap member to the lead receiving member.